MG is an intelligent boy. One day he was challenged by the famous master called Douer:
if the sum of the square of every element in a set is less than or equal to the square of the sum of all the elements, then we regard this set as ”A Harmony Set”.
Now we give a set with $n$ different elements, ask you how many nonempty subset is “A Harmony Set”.
MG thought it very easy and he had himself disdained to take the job. As a bystander, could you please help settle the problem and calculate the answer?